1. Filed of the Invention
The present invention relates to a power generation system utilizing a fuel cell (hereafter referred to as fuel cell system). Specifically, it relates to a technique for removing fluorine from water circulating through a water circulation path of the fuel cell system.
2. Description of the Related Art
In fuel cell systems, hydrogen obtained by reforming fuel such as methanol, gasoline, etc. is supplied to a negative electrode (fuel electrode) of the fuel cell, and air is supplied to a positive electrode (air electrode). An electrochemical reaction between the hydrogen and oxygen is caused to take place within the fuel cell, thus generating power. Among fuel cell systems, it is expected that so-called polymer electrolyte-type fuel cells (PEFC), which use a polymer electrolyte membrane that conducts hydrogen ions, will readily constitute a compact and highly efficient power generating system. PEFC is expected to be an appropriate power source for electric cars, etc.
Polymer electrolyte-type fuel cells usually utilize a perfluoro-type fluorocarbon polymer ion exchanging membrane (for example, a membrane formed from perfluorocarbon sulfonic acid having the sulfonic acid group as the ion exchanging radical). It is essential that this type of membrane remains wet for maintaining sufficient conductivity of hydrogen ions.
Furthermore, since fuel cells use an exothermic reaction between hydrogen and oxygen, heat tends to be produced. However, the optimal operating temperature of polymer electrolyte-type fuel cells is 80° to 100° C. Consequently, cooling must be performed. Usually, cooling water is introduced through the fuel cells.
Moreover, the reaction between hydrogen and oxygen forms water at the positive electrodes (air electrode) of the fuel cells. The water that is formed within the fuel cells must be removed from the fuel cells.
In power generating systems mainly composed of polymer electrolyte-type fuel cells, the polymer electrolyte membranes must remain wet, the fuel cells must be cooled, and water formed at the positive electrodes must be discharged. In order for these functions to be performed, a water circulation path passes through a fuel cell main body (stack).
Since fuel cell systems have become more compact in recent years, water circulation paths that are as simple as possible have been devised. For example, Japanese laid open patent publication 6-275284 presents a polymer electrolyte-type fuel cell wherein a portion of the cooling water flowing a cooling water passage formed within a gas separator is supplied to a negative electrode (fuel electrode), and water formed at a positive electrode (air electrode) is guided into the cooling water passage.
In this type of power generating systems utilizing fuel cells, providing a water circulation path along which the cooling water circulates allows all of the followings to be realized: the cooling water circulates; the polymer electrolyte membrane remains wet; and the water that has been formed is discharged.